Code committed in https://www.drupal.org/node/2450897 not adding 'views display' cache context to row cache data.
It only adds 'view' cache context. This produces strange behaviour when you try to preprocess a views field (hook_preprocess_views_view_field()).
If you have exposed filter in the view and do some logic in your preprocess hook based on exposed filter value - this hook will be executed only once per row field, for first value of exposed filter. All other requests will return cached version when you change exposed filter value. You might not reproduce this bug because one of 'row' cache keys is a hash of row data. So it reproduces only when the row is the same but exposed filter value is different.